The present invention relates to a retractable treatment instrument to be inserted into an instrument-inserting channel of an endoscope.
In general, the treatment instrument includes a front-end treatment member connected to a leading end of an operation wire inserted into a flexible sheath to be movable along an axial direction of the flexible sheath. The front-end treatment member is capable of protruding from a front end of the flexible sheath and retracting into the flexible sheath. It is also possible to adjust a projected length of the front-end treatment member from the front end of the flexible sheath by moving the operation wire in the axial direction. Examples of such a treatment instrument are disclosed in Japanese Patent Provisional Publications No. 2002-113016 (hereafter, referred to as JP 2002-113016A) and No. 2005-270240 (hereafter, referred to as JP 2005-270240A).
The retractable treatment instrument disclosed in JP 2002-113016A is provided with a screw member at the front end of the flexible sheath so that the screw member is used to adjust the projected length of the front-end treatment member from the front end of the flexible sheath. According to the retractable treatment instrument disclosed in JP 2005-270240A, the front-end treatment member is configured to have a wide part at its proximal portion. The width of the wide part of the front-end treatment member is larger than an inner diameter of a flexible tube (flexible sheath) so that the projected length of the front-end treatment member from the leading end of the flexible tube can be kept at an adjusted position by friction between an edge of the wide part and the inner surface of the flexible tube.
According to the configuration disclosed in each of JP 2002-113016A and JP 2005-270240A, the projected length of the front-end treatment member can be adjusted at a desired length. Further, since the front-end treatment member can be fixed stably at the adjusted position, the projected length of the front-end treatment member is not changed by a force applied to the front-end treatment member when the front-end treatment member touches tissue of a body cavity during a diagnostic operation.
However, the treatment instrument disclosed in JP 2002-113016A has a drawback that the structure of the treatment instrument becomes inevitably complicated if the requirement for providing the screw member at the front end of the flexible sheath is achieved. In general, providing a screw member at the front end of the flexible sheath of the treatment instrument whose diameter is approximately 2 mm makes it impractical to use the treatment instrument for endoscopes. In addition, it is impossible to adjust the projected length of the front-end treatment member while the front portion of the treatment instrument is in the body cavity. Therefore, it is necessary to withdraw the treatment instrument from the instrument-inserting channel of the endoscope to adjust the projected length of the front-end treatment member.
The treatment instrument disclosed in JP 2005-270240A has a drawback that the manufacturing cost of the front-end treatment member is relatively high because it is necessary to form the wide part at the proximal portion of the front-end treatment member. In addition, there is a possibility that friction between the edge of the wide part and the inner surface of the flexible tube decreases considerably due to permanent deformation of the cross-sectional shape of the flexible tube caused in the direction in which the inner surface of the flexible tube is elongated by the wide part of the front-end treatment member. If the friction decreases as mentioned above, it becomes difficult to keep the projected length of the front-end treatment member at the desired length stably.